The invention relates to a method for processing a presence signal in a hands-free vehicle access system equipped with capacitive sensors. A hands-free access system performs a series of functions for the comfort of the driver or owner of the vehicle. It results in a pleasant or “magical” effect: when one of the electronic keys authorized to open this vehicle approaches said vehicle a series of signals are transmitted by the vehicle, referred to as welcome signals, and the doors of this vehicle are unlocked immediately. A further function is subsequently added to these two first functions: it is possible to start the vehicle whilst the electronic key remains in a pocket or bag. A final function added to these three first functions lies in confirming the request to unlock the door with the supplementary use of sensors that detect the presence of a hand held on the handle of the vehicle and thus detect the intention of the owner to access his vehicle.
This type of hands-free access generally functions by means of radio communications between a central unit installed in the vehicle and the electronic key as well as wired communications between presence sensors (for detection of a hand on a vehicle handle) and the central unit. The radio communications are in the low-frequency range, for example 125 kHz, for the emission from the central unit to the electronic key and are in the radio frequency range, for example 433 MHz or 315 MHz, for the emissions from the electronic key to the vehicle.
In general, the presence sensors are installed in the handles of the openings (door or lid of the luggage compartment) of a vehicle, the handles also each accommodating a radio frequency antenna for receiving signals originating from the electronic key and destined for the central unit. The electronic keys are also equipped with transmitting/receiving radio frequency antennas in order to communicate with the radio frequency antennas of the central unit.
The hands-free access as exists today thus comprises the joint use of presence sensors for detecting a hand held on a handle and the remote recognition of the electronic key via radio communications.
This operating principle is described in particular in patent document US 2012/0249291, which proposes the joint use of radio communications and infrared sensors, with the following exemplary embodiment. The vehicle awaiting the arrival of an authorized key verifies the arrival of this key via interrogations transmitted via radio. When the approach of a key is confirmed, the sensors await the detection of a hand. If the detection of the hand meets certain requested conditions, and if the key remains in the vicinity of the vehicle, the unlocking of the doors is authorized.
This method has the disadvantage of requiring the use of infrared sensors. These sensors are not very reliable, since it is imperative that the object to be detected has good reflectivity. Moreover, these sensors are likely to give bad results if it is raining. Their use therefore is not advantageous.
Further exemplary embodiments of hands-free access systems comprise capacitive sensors. However, the use of these capacitive sensors is disturbed by the radio communications of the radio frequency antennas. The capacitive sensors may then give erroneous orders to the central unit of the vehicle. A solution to this problem lies in interrupting the electrical power supply to the capacitive sensors during the radio transmissions of the radio frequency antennas, thus rendering the capacitive sensors non-operational during these transmission periods.
Patent application FR 2 915 838 presents a further hands-free access approach and provides the following solution to the disturbance affecting the capacitive sensors as a result of the radio communications. This solution lies in blocking, at the central unit, the signals originating from the capacitive sensors when these signals are transmitted at the same time as the radio signals. In addition to the same disadvantage as in the previous solution with regard to communication interruption, this blocking requires a software modification in the central unit.
This type of method, comprising both radio communications between keys and central unit and wired communications between capacitive sensors and central unit for hands-free access, is illustrated in FIG. 1. Throughout this method, the information transmitted by the capacitive sensors is then stopped during the radio emissions. The method starts with the step of nominal operation 20 called “Start”. This step is followed by a step of switching to a low-energy consumption mode “W” 22 of the central unit so as to save the electrical energy of the vehicle, until the presence of an electronic key “K” in the vicinity of the vehicle has been confirmed during the test 26. As long as no electronic key is recognized during the test 26, the method returns to the step Start 20. When the presence of an electronic key is recognized during the test 26, the method switches the central unit into a high-energy consumption mode “W W”—step 28—so as to be able to ensure encrypted identification request dialogue with said electronic key.
The identity request test 30 concerns the success of the encrypted dialogue between the central unit and the electronic key for the identity request “Id?” of this electronic key. If this test is unsuccessful the process returns to the Start 20. If it is successful, that is to say if the identity is effective, the method awaits the detection of a hand by the capacitive sensor (presence detection test 34), then determines whether this detection is validated by the central unit during the test 36. The validation test may relate for example to the fact that the capacitive sensor that has detected a hand is in the same handle as the antenna having detected the electronic key. In the case of a negative response “N” to at least one of these two presence tests 34, 36, the method returns to the Start 20. In the case of a positive response “O” to these two tests, the method terminates at step 38 “End” with the unlocking of the door in question or of all of the doors of the vehicle depending on the parameterization of the method.
However, this type of method has a significant disadvantage: because the capacitive sensors are disturbed during the radio communications, it is advantageous to stop the information transmitted thereby during said radio communications, and this places the user in front of a “wall effect”. This wall effect corresponds to an abnormally long period during which the user must grasp the handle of a door before the door is successfully unlocked.